The present invention relates to windows on aircraft and, in particular, relates to devices for attaching windows to high performance military aircraft. These windows are used for optical systems such as cameras, sensors, gimbals, etc.
As is well known to those skilled in the art, windows of this type must be mounted in such a manner that the connection between the window and the wall can withstand the stresses exerted on it by the net pressure thereabout, that the connection between the window and the wall is leakproof and does not allow the air to escape. Further, since such windows consist of a material different from the material constituting the walls of such compartments, the dimensions of these windows change differently under the influence of temperature changes. For instance, if the windows consist of transparent artificial resin, their expansion under the influence of temperature rises is considerably greater than that of the walls of the compartment which as a rule consist of a light metal. If the connection of such windows with the wall is unyielding, this connection is not only acted upon by the forces resulting from the net pressure, but also by forces arising in consequence of the difference in expansion and contraction of the windows on the one hand and the walls on the other hand. Consequently, this connection must be so chosen as to be able to withstand comparatively great forces. This is especially true in military applications where many extreme environments are encountered and the components must be kept as small and as lightweight as possible.
A prior device for mounting curved windows to aircraft walls, for example, is a clamping ring having an inwardly slanting flange. This flange bears directly upon the window. Both the window and the clamping ring are in contact with the aircraft wall. An O-ring is placed between the window and the aircraft wall at the point of contact to maintain a pressure and liquid seal. The clamping ring is bolted to the aircraft wall.
The environment inside the optical system is normally controlled to prevent moisture from condensing on the optics as the aircraft changes altitudes, speeds, etc. To prevent this, the optical system environment is filled with dry nitrogen, for example. This results in pressure differentials between the controlled environment (Pc) and the outside environment (Po). A net force therefrom puts additional stress on the window. Although the clamping ring with a flange is simplest to fabricate, it has the undesirable effect of restraining rigidly the window in the x and y directions, the x-direction being parallel to the aircraft wall. If there was a uniform temperature expansion coefficient between the components, the above clamping ring would be sufficient, but because of differences, the window can either shrink and become lose or expand and become over stressed because of a nonyielding clamping ring.